JPS62288866A - Electrostatic latent image producing device for detecting picture density - Google Patents

Abstract

PURPOSE:To simplify a structure, by providing a reference toner image producing light source which uniformly illuminates a small part of the surface of a photosensitive body separately from the light source which forms the latent image of a recording picture on the surface of a photosensitive body. CONSTITUTION:At appropriate timing other than the picture recording timing by means of picture signals, an electrostatic latent image for picture density detection is produced on the photosensitive body 1 by means of a reference toner image producing light source 5. In the case of inversional development, only the exposed part of the photosensitive body 1 is developed and a toner image is formed. Therefore, the reference toner image producing light source 5 is used for the exposing part of the photosensitive body 1 necessary only for producing a reference toner image for density detection and, since the reference toner image is extremely small, a small light source can sufficiently be used as the light source 5. Accordingly, any complicated circuit configuration, such as a light quantity control circuit, circuit for producing picture signal to be used for generating prescribed pattern signals, etc., becomes unnecessary.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Industrial Application Field The present invention relates to a method for forming a reference toner image for image density detection on a photoreceptor in a laser printer or other electrophotographic printer. The present invention relates to an electrostatic latent image creation device for image density detection that creates an electrostatic latent image.

2. Description of the Related Art Conventionally, in an electrophotographic copying machine, it is known that a reference toner image is formed on a photoreceptor and the density of the image is detected to control the density of a recorded image. To form this reference toner image, a reference density piece is provided in advance on a part of the document table of the copying machine, and this reference density piece is exposed onto the surface of the photoconductor using an optical system for reading the original. This is done by forming a corresponding electrostatic latent image on the strip and then developing it into a toner image. The reference density pieces used here include a solid black image, a gray one with an optical reflection degree of 1.2 or less, and a combination of white and black areas as seen in Publication of Utility Model Publication No. 60-4188. Some examples are known.

Recently, as a method of forming an electrostatic latent image on the surface of a photoreceptor, a laser beam or other light source is used instead of the optical system for reading originals in a copying machine, and the light emitted from this light source is irradiated onto the surface of the photoreceptor. An electrophotographic printer has been developed that forms an electrostatic latent image on the surface of a photoreceptor by controlling both irradiation and non-irradiation according to input image signals, and then develops and transfers that latent image. It is used. For example, in a so-called laser printer that uses a laser beam as the light source, an electrostatic latent image is formed by scanning the surface of a photoreceptor with a polygon mirror or the like with a laser beam that is blinked or modulated according to an image signal. There is. Furthermore, in a so-called LED printer that uses LED lamps, an electrostatic latent image is formed by individually blinking a large number of LED lamps arranged in an array in accordance with an image signal. Furthermore, in so-called LCS printers, in which a light source such as a fluorescent lamp is equipped with a liquid crystal display (LC8) array, a large number of liquid crystal shutters arranged in an array are opened and closed individually according to image signals. An electrostatic latent image is formed by opening or closing the irradiation of the fluorescent light onto the surface of the photoreceptor.

Image density control is also necessary in these electrophotographic printers, and it is conceivable to form a reference toner image on the surface of a photoreceptor and detect its density, as in the above-mentioned copying machine. In this case, to form an electrostatic latent image for image density detection, a reference density piece such as that used in copying machines is used, which is illuminated with a light source, and the reflected light is directed onto the photoreceptor using an optical device. The method of forming an image on the latent image requires a large amount of optical equipment such as a light source and a lens just for the purpose of forming the latent image, and is not practical. Therefore, in view of the fact that copying machines use an optical device for image formation to create an electrostatic latent image for detecting image density, laser printers use a laser beam scanning device, and LED printers use a laser beam scanning device. It is conceivable to use an LED head or an LCS head in an LCS printer to create an electrostatic latent image for image density detection.

Problems to be Solved by the Invention However, with this configuration, although the optical device for the reference density strip can be saved, the control circuit for controlling the blinking or light intensity of the laser beam or LED lamp becomes large.
There was a problem that it was not possible to achieve sufficient economic effects.

The problem of increasing the number of control circuits will be explained below.

In a laser printer, in order to use a laser beam scanning device to create an electrostatic latent image for image density detection, it is necessary to generate an image that generates a predetermined signal so that an electrostatic latent image of the desired image is formed on the photoreceptor. The signal generating circuit may be connected to the laser emitting circuit to control the laser emitting circuit. By developing the electrostatic latent image created by this method, a reference toner image for image density detection is formed. The reference toner images formed in this case include a low-density, non-patterned reference toner image created by adjusting the amount of laser light scanning the photoreceptor, and a white part formed by blinking the laser light. There are two reference toner images with patterns created by combinations of black parts; an example of the latter is disclosed in Japanese Patent Laid-Open No. 60-4936.
There is Publication No. 3. Of these two reference toner images, when using a plain, low-density reference toner image without a pattern, a light amount control circuit is required to control the amount of laser light to a smaller value than when creating the image. becomes. On the other hand, when using a reference toner image with a pattern, it is necessary to generate a complicated pattern signal using an image signal generation circuit in order to create a predetermined pattern image. becomes complex, and in both cases, the costs are non-negligible.

In addition, in order to use the LED hand to create an electrostatic latent image for detecting image density in an LED printer, as in the case of a laser printer, an image signal generation circuit that generates a predetermined signal is connected to the LED drive circuit. All you have to do is control the LED drive circuit. In this case as well, the reference toner image is LE
There are two types of toner images: a low-density reference toner image with no pattern created by adjusting the light intensity of the D lamp, and a reference toner image with a pattern created by a combination of white areas formed by blinking individual LED lamps. . Then, as in the case of a laser printer, there is either a light 1 control circuit that controls the light intensity of the LED lamp to a smaller value than when creating an image, or an image signal generation circuit that generates a predetermined pattern signal. The cost of my need becomes too much to ignore.

In addition, in LCS printers, a low-density pattern is created as a reference toner image by adjusting the light intensity of a fluorescent light source lamp and closing the liquid crystal shutter in areas unnecessary for creating the reference toner image. There are two types of reference toner images: a reference toner image without a pattern, and a reference toner image with a pattern formed by a combination of white and black areas formed by opening and closing individual liquid crystal shutters. Also in this case, a light amount control circuit for reducing the light amount of the fluorescent lamp,
Either a range specification circuit that determines the range of the reference toner image and controls opening and closing of the liquid crystal shutter, or an image signal generation circuit that generates a predetermined pattern signal is required, and the cost of this cannot be ignored. Become.

The present invention has been made in view of the above-mentioned problems, and does not require complicated devices such as a light amount control circuit or an image signal generation circuit, and has a simple configuration that allows a standard for image density detection to be formed on a photoreceptor. An object of the present invention is to provide an electrostatic latent image forming device for detecting image density in an electrophotographic printer, which forms an electrostatic latent image for forming a toner image.

Means for Solving the Problems In order to solve the above-mentioned problems, the first invention of the present application uses a light source that uniformly illuminates a small portion of the surface of the photoreceptor, separately from the light source that forms the latent image of the recorded image on the surface of the photoreceptor. A light source for creating a reference toner image that illuminates the toner image is provided.

According to the above-described structure, the light source for creating a reference toner image illuminates a small portion of the surface of the photoreceptor to form an electrostatic latent image, and by developing this, a reference toner image is created. can do.

At this time, by setting the illuminance of the light source for creating the reference toner image to a value lower than the amount of light irradiated during normal image formation, it is possible to form a reference toner image with low density and no pattern. When a recording light source and optical device are used to create an electrostatic latent image for creating a reference toner image, complex light amount control circuits or image signal generation circuits to generate predetermined pattern signals are required. Since no electrical circuit configuration is required, the structure can be simplified.

Problems to be Solved by the Invention By the way, as described above, the surface of the photoreceptor is illuminated with a constant illuminance to create an electrostatic latent image, and the density of the reference toner image obtained by developing this is detected. It has been found that when performing density adjustment, a new problem arises in laser printers and LED printers in that they are susceptible to environmental temperature changes.

The inventor investigated the cause of this problem and found that the density of the reference toner image is caused by the temperature change of the photoreceptor.

The reason for this will be explained below.

Semiconductor lasers used as light sources for laser printers have an oscillation wavelength in the near-infrared region. Furthermore, red light is used in LEDs used as light sources for LED printers because red light has an extremely high luminous efficiency with respect to the applied current. For this reason, the photoreceptors used in these are subjected to infrared light or red light sensitization treatment. Because of this sensitization process, the sensitivity changes more widely with respect to environmental temperature changes than in conventional photoconductors for copying machines.

Figure 6 shows laser light or LE irradiated onto the photoreceptor surface.
7 is a graph showing the relationship between the amount of light from a D lamp and the surface potential of a photoreceptor after exposure. As the amount of irradiated light increases, the surface potential decreases, but the degree of the decrease varies depending on the temperature of the photoreceptor, and for the same amount of light, it is greater at a high temperature than at a low temperature.

As the image recording light, two values are used: an ON state with the light amount -P in FIG. 6, and an OFF state. For example, when black development is performed using a reversal development method, the light amount = P corresponds to a black image portion, and the light amount of zero (ie, light source 0FF) corresponds to a white image portion. When creating a low constant density reference toner image without a pattern as a reference toner image for image density detection, the reference toner image creation range is irradiated with light having an intensity of a value Q lower than the amount of light irradiated during image recording. carried out by However, since the sensitivity curves differ between low temperatures and high temperatures, the surface potential after exposure is not constant, such as vH at low temperatures and vL at high temperatures.

This situation is illustrated in FIG. When the amount of irradiated light is P and when the amount of light is zero (no light emitted), there is little influence from changes in the temperature of the photoreceptor, and the surface potential is maintained at a roughly constant value. However, when the light amount Q is smaller than P, the surface potential is high at low temperatures and low at high temperatures as shown in the figure, and the optical reflection density of the reference toner image obtained by reversing this development is:
Since the result is that it becomes lighter at low temperatures and darker at high temperatures, the electrophotographic process conditions to be controlled, such as the toner concentration in a two-component developer, are not accurately reflected.

Furthermore, if regular development is performed instead of reversal development, exposure for the reference toner image will be performed near the light amount = R in FIG. 6, but in this case also, as shown by the dotted line in FIG. The optical reflection density of the reference toner image after development becomes darker at lower temperatures and lighter at higher temperatures, which is just the opposite of the result in the case of reversal development. A problem arises in that the target electrophotographic process conditions, for example, the toner concentration in the two-component developer, are not correctly reflected. Such variations in surface potential after exposure due to temperature occur not only when a laser beam or an LED is used as a light source, but also when other light sources are used.

The second invention of the present application was made in view of this new problem, and it is possible to properly reflect the electrophotographic process conditions to be controlled, such as the toner concentration in a two-component developer, regardless of changes in environmental temperature. An object of the present invention is to provide an electrostatic latent image forming device for image density detection of an electrophotographic printer, which is capable of forming a reference toner image.

Means for Solving the Problems The second invention of the present application provides a reference toner imaging light source that uniformly illuminates a small portion of the surface of the photoreceptor, separate from a light source that forms a latent image of a recorded image on the surface of the photoreceptor. and a temperature detecting means is arranged in contact with or close to the photoreceptor, and the light amount of the reference toner image forming light source is controlled according to the temperature detected by the temperature detecting means. be.

Operation The second invention of the present application is capable of controlling the light amount of the light source for creating a reference toner image according to the sensitivity change of the photoreceptor due to the temperature change due to the above-mentioned configuration. It becomes possible to create an electrostatic latent image, and it creates an electrostatic latent image to create a reference toner image that appropriately reflects the electrophotographic conditions to be controlled, such as the toner concentration in a two-component developer. becomes possible.

Embodiments Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a laser printer equipped with an electrostatic latent image forming device for image density detection according to an embodiment of the present invention, in which 1 is a photoreceptor, 2 is a charger, and 3 is a laser scanning device (see FIG. 4 is a developing device. 5 is a light source for creating a reference toner image that uniformly illuminates a small portion of the surface of the photoreceptor 1 and creates an electrostatic latent image for use as a reference toner image for image density detection; I am receiving it. Details of its structure will be described later.

A temperature detector 6 is placed near the photoreceptor 1 and detects the temperature of the photoreceptor 1 or the temperature around it. A temperature detection circuit 7 is connected to the temperature detector 6, and provides a signal corresponding to the detected temperature to a power supply control circuit 8 as an input. The power supply control circuit 8 receives this signal and determines the amount of power to be supplied by the power supply 9.

10 is a reference toner image formed on the photoreceptor 1 for detecting image density; 11 is an LED that illuminates the reference toner image 10;
A light source such as a lamp, 12 is a light receiving element that receives reflected light from the reference toner image 10, and an image density detection circuit 13 is connected to this light receiving element 12.

On the other hand, the developing device 4 is provided with a toner replenishing device 16 and a toner replenishing motor 15 for driving the toner replenishing device 16.
5 is controlled by a toner replenishment circuit 14 which receives a signal from an image density detection circuit 13. In addition,
Although not shown, recording paper supply means, transfer means, photoreceptor surface cleaning means, etc. are arranged around the photoreceptor 1 to carry out a normal electrophotographic process.

Next, the operation of the apparatus having the above configuration will be explained.

Photoreceptor 1 rotates in the direction of arrow A, and after its surface is uniformly charged by charger 2, image recording light 3
An electrostatic latent image is formed based on the image signal input to the printer. The timing of forming an electrostatic latent image using an image signal is controlled according to the positional relationship with the recording paper supplied to the photoreceptor 1, and the created electrostatic latent image is developed with a developing device 4. A recording paper is placed over the resulting toner image, the toner image is transferred to the recording paper, and is permanently fixed on the recording paper through a fixing process.

On the other hand, an electrostatic latent image for image density detection is created on the photoreceptor 1 by the reference toner image creation light source 5 at an appropriate timing other than the image recording timing based on the image signal described above. In this embodiment, development is performed using a reversal development method, and only the exposed portion of the surface of the photoreceptor 1 is developed to form a toner image. Therefore, the light source 5 for creating the reference toner image only needs to be able to expose the surface of the photoreceptor of a size necessary for the reference toner image for density detection.
In addition, since the reference toner image may be extremely small, the light source 5
A small one is sufficient. The electrostatic latent image created by the light source 5 is developed by the developer 4 to become a reference toner image 10. The amount of power supplied to the light source 5 at this time is determined by the power supply control circuit 8, and is set as low as possible compared to the image recording light according to the reference density of the desired reference toner image. Note that details will be described later.

The created reference toner image 10 changes as the photoreceptor 1 rotates.
It is irradiated by a light source 11 for image density detection, and the reflected light enters a light receiving element 12. Output to. Toner supply control circuit 1
4 determines whether or not toner should be replenished from this signal;
The rotation and stop of the toner replenishment motor 150 is controlled, and the toner replenishment by the toner replenishment device 16 is controlled. As a result, the toner concentration in the two-component developer in the developing device 4 is maintained within an appropriate range.

Next, the light source 5 for creating a reference toner image used in this embodiment
I will explain in detail.

FIG. 2 is a sectional view showing one embodiment of the light source 5 for creating a reference toner image. 17 is a light source lamp, which is covered with a hood 18. The hood 18 has an opening 18A facing the surface of the photoreceptor 1, and is configured such that a small portion of the surface of the photoreceptor can be illuminated through the opening 18A.

The inner wall of this hood 18 is finished with a matte white painted surface so that light is reflected and scattered, and the light from the light source lamp 17 becomes almost uniform light with no unevenness in brightness.
The surface of the photoreceptor 1 is illuminated and exposed. Here, the opening 18A of the hood 18 may be in the form of a slit with a necessary depth depending on the size of the desired reference toner image, and the light source lamp 17 simply exposes the photoreceptor through this opening 18A. It is good, so a small amount of light is sufficient.

Next, the amount of power supplied to the reference toner image forming light source 5 determined by the power supply control circuit 8 of this embodiment, and therefore the amount of light irradiated onto the surface of the photoreceptor by the light source 5 will be explained in detail.

FIG. 3, like FIG. 6, is a graph showing the relationship between the amount of light irradiated onto the photoreceptor and the surface potential after exposure. Now, suppose that the appropriate surface potential of the electrostatic latent image for image density detection is V.
. Suppose it was. At this time, the surface potential of the photoreceptor is kept at a nearly constant V. In order to maintain this temperature, it is necessary to change the amount of irradiation light depending on the temperature change of the photoreceptor or its vicinity.

That is, the temperature of the photoreceptor or its vicinity is high (tH
It is necessary to set the irradiation light amount to QL when the temperature is ), and to set the irradiation light amount to QH when the temperature is low (11,). Figure 4 shows a constant surface potential V. This figure shows the relationship between the amount of irradiated light Q (t) needed to obtain Q (t) and temperature. The relationship shown in FIG. 4 is converted into supply power, that is, supply voltage, supply current, or both, and is input into the supply power control circuit 8 in advance. The power supply control circuit 8 calculates a value obtained by converting the irradiation scene Q(t) into a power supply distortion according to the temperature signal from the temperature detection circuit 7, and controls the power supply 9 based on the calculated value. Therefore, the amount of irradiation light when creating an electrostatic latent image for image density detection is controlled by the calculated irradiation light ff1Q(t). zu, always V. is maintained.

FIG. 5 is a graph showing the relationship between photoreceptor temperature, surface potential, and irradiation light amount for obtaining a constant surface potential. As the temperature of the photoreceptor increases, the amount of light necessary for the light source for creating an electrostatic latent image for image density detection, and therefore the amount of power supplied, decreases.

This example shows the case of a reversal development method, but in the case of a regular development method, of the charges on the photoreceptor surface, the portions of the charges that do not contribute to image recording or reference toner image creation are erased. A separate static electricity elimination lamp is required for this purpose.

Furthermore, although the above embodiments show the case where the present invention is applied to a laser printer, the present invention is not limited to this case, but can also be applied to LED printers and LCS printers. however,
Since the photoreceptor used in the LCS printer has relatively little change in sensitivity due to temperature changes, the amount of power supplied to the light source 5 for creating the reference toner image is constant, and the temperature detector 6 and its related temperature detection circuit 7, power supply control. The circuit 8 may be omitted.

Effects of the invention As is clear from the above explanation, the first invention of the present application has the following effects:
Separately from the light source for image recording, there is a light source for creating a reference toner image that uniformly illuminates a small portion of the photoreceptor surface, so by illuminating the photoreceptor surface with this light source, the reference toner image A light amount control circuit or a predetermined pattern, such as when a light source and optical device for image recording are used to create an electrostatic latent image for creating a reference toner image. This eliminates the need for a complicated electric circuit configuration such as an image signal generation circuit for generating signals, and has the effect that the structure can be simplified.

Further, in the second invention of the present application, in addition to the light source for creating a reference toner image, a temperature detecting means is disposed in contact with or in close proximity to the photoreceptor, and the reference Since it is configured to control the light intensity of the light source for creating a toner image, it is possible to control the light intensity of the light source for creating a reference toner image in accordance with changes in the sensitivity of the photoreceptor due to temperature changes. It is possible to always create an electrostatic latent image with a constant potential regardless of the electrophotographic conditions to be controlled, such as the static potential needed to create a reference toner image that properly reflects the toner concentration in a two-component developer. This has the effect of making it possible to create an electric latent image.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic configuration of a laser printer using an electrostatic latent image creating device for image density detection according to an embodiment of the present invention, and FIG. 2 is a light source for creating a reference toner image used in the above embodiment. 3 is a graph showing the relationship between the irradiation light amount and the photoreceptor surface potential after exposure in the above example, and FIG. 4 is a graph showing the relationship between the photoreceptor surface potential and photoreceptor temperature in the above example. Graph showing the amount of light as a parameter, 5th
The figure is a graph showing the relationship between the amount of irradiation light necessary to obtain a constant surface potential and the temperature of the photoreceptor in the above example, and Figure 6 shows the relationship between the amount of irradiation light and the photoreceptor surface potential on the photoreceptor of a general laser printer. FIG. 7 is a graph showing the relationship between the photoreceptor temperature and surface potential in a conventional example, using the amount of irradiated light as a parameter. DESCRIPTION OF SYMBOLS 1... Photoreceptor, 3... Image recording light, 4... Developing device, 5... Light source for creating reference toner image, 6... Temperature detector, 10... Reference toner image, 11 ...Light source, 12.
...Light receiving element, 15...Toner replenishment motor, 16...
- Toner supply device, 17... light source lamp, 18...
Hood, 18A... Name of opening agent Patent attorney
Toshio Nakao and 1 other person l Robber #Atsu S 3rd picture of Gokou t□ 4th Waheko Chienha □ Drip 2i Q Picture of light Honto Kokanno (-u, (high)) 6th Diagram, Kaya i□

Claims (2)

[Claims] (1) Image density characterized by having a light source for creating a reference toner image that is provided separately from a light source that forms a latent image of a recorded image on the surface of the photoreceptor and uniformly illuminates a small portion of the surface of the photoreceptor. Electrostatic latent image creation device for detection. (2) A light source for creating a reference toner image that is provided separately from a light source that forms a latent image of a recorded image on the surface of the photoreceptor and uniformly illuminates a small portion of the surface of the photoreceptor, and a light source that is in contact with or in close proximity to the photoreceptor. An electrostatic latent image for detecting image density, characterized in that it has a temperature detecting means disposed at the temperature detecting means, and a means for controlling the light amount of the reference toner image forming light source according to the temperature detected by the temperature detecting means. Creation device.